losabio lopez, a decorated machine gunner who served tours of duty in iraq and afghanistan was the man who gunned down two of his colleagues. they were both killed by the tactics instructor. a relationship dispute is believed to be behind the shooting. to ban or not to ban has been the question on capitol hill and in communities across the countries. while a national assault weapons ban may have been all by killed in the senate last week, the fight isn't over. a group of mayors led by michael bloomberg is starting a national campaign ad this week hoping to force congress to act. but gun supporters are firing back. athena jones has more. >> they are stepping up their campaign to try to win support for new gun measures. >> i believe in the second amendment and i'll fight to protect it. but with rights come responsibility. >> mayors against illegal guns, led by new york mayor michael bloomberg, is pouring $12 million into ads like these to push congress to act on guns. >> closing loopholes will stop criminals and the dangerously mentally ill from buying guns. >> reporter: here's the mayor